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Why regenerative braking belongs on the brake pedal

Discussion in 'Model 3' started by JeffC, May 25, 2016.

  1. JeffC

    JeffC Member

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    Exactly right. It sounds like they're also simulating slight automatic transmission drag.
     
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  2. JeffC

    JeffC Member

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    Tesla can coast by balancing the throttle between acceleration and braking. Coasting by default with the throttle not pressed, i.e., without needing to balance the throttle is better. Low Regen on Teslas is more like that, but still has some regen off throttle.
     
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  3. S'toon

    S'toon Knows where his towel is

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    Americans also spell words such as honour, armour, and colour without the u. Doesn't mean they spell correctly according to the rest of the English speaking world. :p
     
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  4. ChooseGreen

    ChooseGreen Member

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    Interesting read. I didn't quite grasp why front-wheel regen off of the throttle is a bad idea. If one has a Tesla D variant on a very slippery road and one releases the throttle aggressively, I could see how the wheels could lose traction with the road surface. I am not intimately familiar with Tesla's traction control systems, but isn't it equipped to deal with such a situation?

    Though I have never driven an EV in marginal traction situations, I like the idea of the braking system being completely separate for peace of mind.

    If one puts the throttle in the position where the energy output is zero whilst travelling downhill, isn't that coasting? If you really want to, you could also flip it into neutral to truly coast, then quickly flip it back into drive when you want to add power or slow down by regen couldn't you?
     
  5. JeffC

    JeffC Member

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    Tesla has tweaked the regen. For example the regen is stronger at lower speeds and weaker at higher speeds.

    The issue is that it's an ergonomic error that could make things worse in emergencies. It's not something that most drivers would even understand how to report (how many drivers know what oversteer is, or how to correct it?).

    Please consider taking a performance driving or racing class if you want to be a safer driver and learn how to control a car in all conditions, including extreme limit conditions that can happen in an emergency (and that happen in every turn in racing).
     
  6. int32_t

    int32_t Tesla Spotter

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    #26 int32_t, May 25, 2016
    Last edited: May 25, 2016
    This thread could get hot fast, look out.

    Anyways, with the respect you requested, I have a few counter-points.

    Personally I am a total fan of single-pedal driving and I think it's the best thing ever. (Talk about simplifying driving -- the "drive" pedal and the "emergency" pedal!) I have driven Teslas and Priuses. Tesla's approach is smoother, and strong regen is highly practical for single-pedal driving. As for the Prius, I haven't noticed the allegedly clunky transition from magnetic to friction braking myself, but I have noted that it's impossible to brake with regen alone. To me that sounds like a waste and a missed opportunity.

    Regarding what you say about "trailing throttle oversteer," sure that could be an issue with a RWD vehicle. However, with AWD Teslas (judging by wk057's research) there's no way traction control is going to let the wheels pop loose from the pavement. It can modulate braking between the front and rear quite easily, and much faster than physics can pull the car around. I am also inclined to believe traction control on RWD Teslas is good enough to prevent this sort of thing anyways.

    In the end, regarding your point about daily driving vs racing and emergency conditions, since the vast majority of driving is normal daily driving for which the single-pedal approach is best suited, why is it a bad thing? The other pedal is still there, ready any time you need it.

    If you want to talk science, I'm pretty sure single-pedal is more efficient than any regen-on-brake system could be simply because of the separation of magnetic/friction braking. Back to vibes and opinion, my general impression is that there's something else behind this. The page you linked to almost comes across as a rant against the one-pedal approach. Is it as simple as a personal preference for two-pedal control? Your website looks a little bit political in places ...

    -- Updated --

    I don't understand what ergonomics have to do with oversteer. Ergonomics: my seating position, the position of controls relative to me, etc. Oversteer: lands squarely in traction control's department and I don't have to care or even know what it is.

    Taking a performance driving / defensive driving class is on my to-do list. It sounds like a good idea.
     
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  7. ratsbew

    ratsbew Active Member

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    I respectfully disagree. I want 100% regnen upon liftoff. I want to know that the instant my foot touches the brake pedal that I'm wasting energy to heat. If the brake is blended regen/friction then I as the driver have no way of knowing how to maximize my regen without using the friction brakes.
     
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  8. JeffC

    JeffC Member

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    #28 JeffC, May 25, 2016
    Last edited: May 25, 2016
    Automatic stability control (traction control) will always try to do the right thing, and usually works correctly in less than extreme conditions. The issue is that getting heavy braking due to having heavy regen on the throttle can lead to a loss of control that the automatic systems may not be able to recover from. At some point, the laws of physics take over. To be clear, this would only happen in extreme limit conditions, such as an emergency. But it's better to have a control design that makes it harder to exceed those limits in the first place, and not get into an emergency.

    Regen integrated with the brakes makes driving simpler and safer. If you want to slow down, you know to use the brake pedal. You can't unintentionally get heavy regenerative braking by lifting off the throttle.

    On a car with regen on the throttle like Teslas or the BMW i3, balancing the throttle position between acceleration and deceleration is the way to coast, exactly as you describe. However on cars where the regen is on the brake pedal instead, it's possible to coast by simply lifting all the way off the throttle (if the control design allows it), which is much simpler to do.
     
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  9. JeffK

    JeffK Well-Known Member

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    This depends on road conditions. Coasting in an automatic uses gasoline as opposed to engine braking and coasting in an EV uses energy to counteract the counter electromotive force as opposed to regen. It's easier to just maintain speed if you wish to "coast".

    Of course slowing down just to speed up again is wasteful so one must judge base of future road conditions (if a hill is coming up etc).
     
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  10. JeffC

    JeffC Member

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    #30 JeffC, May 25, 2016
    Last edited: May 25, 2016
    Regen is always maximized on cars with regen integrated with the brake very early in the brake application.

    How do you get maximum regen in a car with regen integrated with the brakes? Simply start using the brakes. The majority of the early braking is all regen, and it maxes out before significant friction braking happens. You always get maximum regen early on.

    However, the issue I raise is not efficiency but safety in extreme limit conditions such as an emergency.
     
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  11. JeffC

    JeffC Member

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    #31 JeffC, May 25, 2016
    Last edited: May 25, 2016
    Yes, I'm referring to coasting electric motors. I wasn't clear about that.

    Coasting an electric motor means no electric power into or out of the motor.
     
  12. plankeye

    plankeye That Vegan EV Guy

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    I just drove my first Tesla today (P85 MS). The (standard) regen was definitely pretty strong, and surprised me, even though I knew it was strong after reading on this forum. Although, I can see where I would (fairly quickly) get used to it. One thing that makes it not a huge pain is the fact that the accelerator pedal has just the right amount of resistance and "stickiness." Meaning, it's not too easy to press or let up (slippery) and tends to want to stay where you have it. That allows you to ease your foot off slowly without straining your foot to keep the pedal somewhat depressed until you get close enough to a stop to totally left off.

    In a nutshell, I think will grow to like "one pedal driving" when I get my M3. :)
     
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  13. JeffK

    JeffK Well-Known Member

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    I have to be honest I'm going to get a Tesla purely for the acceleration and the regen. I LOVE engine braking and horribly miss having a manual transmission.

    Even though there's only one gear I want the Tesla to behave exactly like a manual in low gear. It's a ton of fun on winding roads.
     
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  14. Red Sage

    Red Sage The Cybernetic Samurai

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    Waitasec... You make a declarative statement or three... But never actually answer the implied question of 'Why?' at all. You just give a link to something else instead. Uhm... I'm not clicking that link. If you have something to say, just say it. What exactly are your 'several reasons', Man? Don't give us a childish, "If you don't know, you betta ask somebody!"
     
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  15. Topher

    Topher Energy Curmudgeon

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    Works fine on a prius. What's complex about the accelerator speeding the car up, and the brake pedal slowing it down? How could it possibly affect brake feel?

    Thank you kindly.
     
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  16. JeffC

    JeffC Member

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    #36 JeffC, May 25, 2016
    Last edited: May 25, 2016
    Thanks for your feedback and trying to be very civil. I'm decidedly not trying to start a flame war, so it's nice to discuss things rationally.

    In understand the benefits of single pedal driving. I tried to explain some of the reasons why it's wrong from the point of view of driver psychology and safety.

    The point about wanting to minimize the use friction brakes is absolutely correct in terms of efficiency, and I agree with it. However in practical implementations of regen integrated with the friction brakes, very little friction braking (if any) is used before the regen is maxed out. It's definitely designed to be efficient. Everyone who designs regen wants to maximize it whether the regen is integrated with the friction brakes or with the throttle.

    Trailing throttle oversteer can happen in any car.

    Traction control can try to keep a car under control, but only within certain limits. At some point if the limits of the tires are exceeded far enough, it can't recover. The laws of physics always win.

    M personal web page has some political parts. I'm a libertarian. I'm in favor of freedom. However that doesn't have anything to do with my position on regen, which is a human factors engineering and vehicle dynamics issue.

    Ergonomics is the science of how people interact with their environment. It definitely includes studying how people use the controls in their cars.
     
  17. JeffC

    JeffC Member

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    Blending the motor braking (regen) with the friction braking can result in strange brake pedal feel if it's not done well, since there are essentially two systems competing for the same work.

    However many implementations integrate regen and friction brakes well; so well that the blending is seamless and imperceptible. Toyota figured out how to do it well by the second generation Prius, for example.
     
  18. JeffC

    JeffC Member

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    Fair point; my essay there is probably too long to post here. That's why I linked to it.
     
  19. JeffC

    JeffC Member

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    #39 JeffC, May 25, 2016
    Last edited: May 25, 2016
    Tesla got many things very right. All of the control feel is good, including the lack of friction in the pedals, pretty good steering feel, etc.

    Try setting the regen to low. It feels more like a typical car.

    BTW I'm told that Autopilot will try to max out regen before using the friction brakes.

    However, that's not really the issue I raise.
     
  20. Red Sage

    Red Sage The Cybernetic Samurai

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    From some of your replies to others here, I get the impression that you want Tesla Motors vehicles to drive more like machines, and less like appliances. Is that a fair assessment?
     

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